In computer numerically controlled grinders (CNC-controlled grinders) the position of a workpiece relative to the position of the grinding tool must be precisely determined so that a programmed grinding procedure will be properly performed on the workpiece. This measurement must be frequently updated because the tool dimensions are continuously altered, thereby changing the zero, or contact, position.
Various conventional procedures exist to solve this problem. In one procedure, for example, the workpiece itself is brought into contact with the grindstone. Sonic or vibration measuring means detect this contact and thus the relative positions of both the workpiece and grindstone are determined and stored simultaneously. However, in this procedure processing of the measured data is relatively expensive. Another drawback is that this procedure cannot detect absolute dimensions of the workpiece or tool. Furthermore, because contact is made between the workpiece and tool, the piece can be indented or scratched by the grindstone. Finally, access to the desired contact point on the workpiece may be impossible due to the radius of the grindstone.
Another method for solving this problem uses a measuring sensor to examine the surface of the workpiece. The workpiece and the sensor are moved toward one another. The measured value is then stored in the CNC-control. Following this measurement, the grindstone diameter is measured, for example with an optical sensing facility. Then the grindstone and the sensor are moved toward one another. In this approach, two separate measurement steps must be taken and two measuring facilities are needed.
A third method is to optically determine the outer contours of the workpiece and the grindstone. For example, laser scanners may sense and transmit this contour data to a computer. The computer then analyzes the data and generates a control program based on the geometries of the workpiece and grinding tool. Such a system detects and compensates for all of the deviations in the workpiece and grindstone, and also performs the measurements while machining takes place. This type of system, however, requires elaborate hardware and software and is therefore extremely expensive.